1. Field of the Invention
The present invention relates to a fuel cell for generating electricity using hydrogen and oxygen and a fuel cell system equipped with a hydrogen storage unit storing hydrogen to be supplied to the fuel cell. More particularly, the invention relates to a technology for controlling the supply of hydrogen to the hydrogen storage unit from outside.
2. Description of the Related Art
A fuel cell is a device that generates electricity from hydrogen and oxygen so as to obtain highly efficient power generation. A principal feature of a fuel cell is its capacity for direct power generation which does not undergo a stage of thermal energy or kinetic energy as in conventional power generation. This presents such advantages as high power generation efficiency despite the small scale setup, reduced emission of nitrogen compounds and the like, and environmental friendliness on account of minimal noise or vibration. A fuel cell is capable of efficiently utilizing chemical energy in its fuel and features environmental friendliness. Fuel cells are therefore envisaged as an energy supply system for the twenty-first century and have gained attention as a promising power generation system that can be used in a variety of applications including space applications, automobiles, mobile devices, and large and small scale power generation. Serious technical efforts are being made to develop practical fuel cells.
Hydrogen, which is fuel for such fuel cells, is gaseous at normal temperature. Hence, even when hydrogen being supplied to a fuel cell should leak at some point in the fuel cell system, a user may not often become aware of it, thus letting part of the hydrogen run to waste. Further, if the supply of hydrogen from outside the fuel cell system is kept on without the user noticing the abnormality of hydrogen leak, then a large amount of hydrogen will leak out and thus be wasted because the hydrogen is normally stored in a hydrogen supply unit under high pressure.
There have been various technologies proposed for preventing hydrogen leaks from a fuel cell system following the detection of the abnormality. In such conventional technologies, hydrogen leaks are typically controlled by the operation of an actuator that closes the valve of a hydrogen cylinder.
When a fuel cell is used as a power supply for a mobile device, it is required that the fuel cell system therefor be small-sized. Use of an actuator in such a fuel cell system tends to make the system structure more complex, thus making its downsizing difficult. Moreover, the drive power of the actuator is large, and therefore it is not desirable that an actuator be used in a fuel cell system for a mobile device.